Ruby to_json对象输出实例变量

Question

I'm using Sinatra and trying to output an object in JSON by using the 'json' gem and calling the .to_json method. I expected the output to be JSON with the symbols in the attr_reader section and their values.

Here's my code. Do I need to do anything special to get this to work?

require "sinatra"
require "json"    

class Foo
  attr_reader :id, :name

  def initialize(id, name)
    @id = id
    @name = name
  end
end

get '/start' do
  content_type :json
  Foo.new(2, "john").to_json
end

All I get from the output is the objects default to_s.

"#<Foo:0x007fe372a3ba80>"

Answer 1

You need to specify a to_json method on your class.

class Foo
  attr_reader :id, :name

  def initialize(id, name)
    @id = id
    @name = name
  end

  def to_json 
    {:id => @id, :name => @name}.to_json
  end
end

Answer 2

Looks like you need a to_hash method

class Foo
  def to_hash
    {:id => @id, :name => @name}
  end
end

Otherwise Foo is not a type recognizable by json.